Abstract: nutrients Article Vitamin D Intake May Reduce SARS-CoV-2 Infection Morbidity in Health Care Workers Tatiana L. Karonova 1, * , Alena T. Chernikova 1 , Ksenia A. Golovatyuk 1 , Ekaterina S. Bykova 1 , William B. Grant 2 , Olga V. Kalinina 1 , Elena N. Grineva 1 and Evgeny V. Shlyakhto 1 1 2 *



 Citation: Karonova, T.L.; Chernikova, A.T.; Golovatyuk, K.A.; Bykova, E.S.; Grant, W.B.; Kalinina, O.V.; Grineva, E.N.; Shlyakhto, E.V. Vitamin D Intake May Reduce SARS-CoV-2 Infection Morbidity in Health Care Workers. Nutrients 2022, 14, 505. https://doi.org/10.3390/ nu14030505 Academic Editor: Roberto Iacone Received: 29 December 2021 Accepted: 21 January 2022 Clinical Endocrinology Laboratory, Department of Endocrinology, Almazov National Medical Research Centre, 194021 Saint Petersburg, Russia; arabicaa@gmail.com (A.T.C.); ksgolovatiuk@gmail.com (K.A.G.); bykova160718@gmail.com (E.S.B.); olgakalinina@mail.ru (O.V.K.); grineva_e@mail.ru (E.N.G.); shlyakhto_ev@almazovcentre.ru (E.V.S.) Sunlight, Nutrition, and Health Research Center, San Francisco, CA 94164-1603, USA; williamgrant08@comcast.net Correspondence: karonova@mai.ru; Tel.: +7-921-310-60-41 Abstract: In the last 2 years, observational studies have shown that a low 25-hydroxyvitamin D (25(OH)D) level affected the severity of infection with the novel coronavirus (COVID-19). This study aimed to analyze the potential effect of vitamin D supplementation in reducing SARS-CoV-2 infection morbidity and severity in health care workers. Of 128 health care workers, 91 (consisting of 38 medical doctors (42%), 38 nurses (42%), and 15 medical attendants (16%)) were randomized into two groups receiving vitamin D supplementation. Participants of group I (n = 45) received water-soluble cholecalciferol at a dose of 50,000 IU/week for 2 consecutive weeks, followed by 5000 IU/day for the rest of the study. Participants of group II (n = 46) received water-soluble cholecalciferol at a dose of 2000 IU/day. For both groups, treatment lasted 3 months. Baseline serum 25(OH)D level in health care workers varied from 3.0 to 65.1 ng/mL (median, 17.7 (interquartile range, 12.2; 24.7) ng/mL). Vitamin D deficiency, insufficiency, and normal vitamin D status were diagnosed in 60%, 30%, and 10%, respectively. Only 78 subjects completed the study. Vitamin D supplementation was associated with an increase in serum 25(OH)D level, but only intake of 5000 IU/day was accompanied by normalization of serum 25(OH)D level, which occurred in 53% of cases. Neither vitamin D intake nor vitamin D deficiency/insufficiency were associated with a decrease in SARS-CoV-2 morbidity (odds ratio = 2.27; 95% confidence interval, 0.72 to 7.12). However, subjects receiving high-dose vitamin D had only asymptomatic SARS-CoV-2 in 10 (26%) cases; at the same time, participants who received 2000 IU/day showed twice as many SARS-CoV-2 cases, with mild clinical features in half of them. Keywords: COVID-19; SARS-CoV-2; vitamin D; 25(OH)D; health care workers Published: 24 January 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in